Rapid maxillary expansion in adults: cranial stress reduction depending on the extent of surgery.

The objective of this study on surgically assisted rapid maxillary expansion (RME) was to examine the extent of stress reduction in the midface and the cranial base with various surgical procedures. Four finite element models of the skull were generated (one without and three with different surgical incisions), in which a virtual RME (5 mm gap width) was simulated. In all four simulations, von-Mises stresses were measured at 30 anatomical structures of the midface and cranial base (in MPa) and compared. The highest von-Mises stresses were measured with the model that did not involve any osteotomies. A reduction of the observed stresses was found after isolated weakening of the zygomaticoalveolar crest on both sides. The model with a complete lateral osteotomy from the piriform aperture to the pterygopalatal junction clearly showed lower stresses than the model with isolated weakening of the zygomaticoalveolar crest. The lowest stress values, however, were seen on the model with a complete osteotomy at the Le Fort I level. In order to prevent complications at the cranial base, surgical assistance is an important aspect of RME in adults. The extent of osteotomies can be varied. The older the patient and the less the bone elasticity, the more extensive should be the surgical weakening in order to minimize the stresses induced at the cranial base and the midface. In older patients, a complete lateral osteotomy from the piriform aperture to the pterygopalatal junction seems to reduce stresses at the cranial base more effectively than isolated weakening of the zygomaticoalveolar crest.